Remove support for multi-line error messages in static error tests.

The static error test format allows an expected error message to contain newlines like:

```dart
some bad code;
// [cfe] The error message
// is two lines long.
```

Here, the expected error is "The error message\nistwo lines long."

This has an unfortunate side effect in that if you have a comment
immediately after a static error expectation, it will be treated as part
of the expected error:

```dart
some bad code;
// [cfe] Error.
// Unrelated comment.
```

This will expect the CFE to report "Error.\nUnrelated comment."

I looked at every static error test and there are no intentional uses
of multi-line expectations. The only two I found were both bugs.

Since this functionality is unused and error-prone, this CL removes it.
Error expectations can only be one line.

Fix #60137.

Change-Id: I7edb1f60a0c87d4160b93810806de49bc8f55b15
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/412185
Auto-Submit: Bob Nystrom <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Johnni Winther <[email protected]>

Author: munificent

pkg/test_runner/lib/src/static_error.dart

@@ -504,10 +504,6 @@ class _ErrorExpectationParser {
   /// "unspecified".
   static final _errorCodeRegExp = RegExp(r"^(?:\w+\.\w+|unspecified)$");
 
-  /// Any line-comment-only lines after the first line of a CFE error message
-  /// are part of it.
-  static final _errorMessageRestRegExp = RegExp(r"^\s*//\s*(.*)");
-
   final String path;
   final List<String> _lines;
   final List<StaticError> _errors = [];
@@ -602,27 +598,6 @@ class _ErrorExpectationParser {
       _advance();
       var sourceLines = {locationLine, _currentLine};
 
-      // Consume as many additional error message lines as we find.
-      while (_canPeek(1)) {
-        var nextLine = _peek(1);
-
-        // A location line shouldn't be treated as part of the message.
-        if (_caretLocationRegExp.hasMatch(nextLine)) break;
-        if (_explicitLocationRegExp.hasMatch(nextLine)) break;
-
-        // The next source should not be treated as part of the message.
-        if (_errorMessageRegExp.hasMatch(nextLine)) break;
-
-        var messageMatch = _errorMessageRestRegExp.firstMatch(nextLine);
-        if (messageMatch == null) break;
-
-        message
-          ..write("\n")
-          ..write(messageMatch[1]!);
-        _advance();
-        sourceLines.add(_currentLine);
-      }
-
       if (source == ErrorSource.analyzer &&
           !_errorCodeRegExp.hasMatch(message.toString())) {
         _fail("An analyzer error expectation should be a dotted identifier.");

pkg/test_runner/test/test_file_test.dart

@@ -336,35 +336,20 @@ num j = "str";
     makeError(line: 10, column: 9, cfeError: "No length.")
   ]);
 
-  // Multi-line error message.
+  // Comment after error message.
   expectParseErrorExpectations("""
 int i = "s";
 /\/      ^^^
 /\/ [analyzer] CompileTimeErrorCode.WRONG_TYPE
-/\/ [cfe] First line.
-/\/Second line.
-    /\/     Third line.
-/\/ [web] Web first line.
-/\/Web second line.
-    /\/     Web third line.
-
-/\/ The preceding blank line ends the message.
+/\/ [cfe] Error message.
+/\/ Unrelated comment.
 """, [
     makeError(
         line: 1,
         column: 9,
         length: 3,
         analyzerError: "CompileTimeErrorCode.WRONG_TYPE"),
-    makeError(
-        line: 1,
-        column: 9,
-        length: 3,
-        cfeError: "First line.\nSecond line.\nThird line."),
-    makeError(
-        line: 1,
-        column: 9,
-        length: 3,
-        webError: "Web first line.\nWeb second line.\nWeb third line.")
+    makeError(line: 1, column: 9, length: 3, cfeError: "Error message."),
   ]);
 
   // Multiple errors attached to same line.
@@ -425,16 +410,14 @@ int n = "s";
 int i = "s";
 /\/      ^^^ /\/# 0: ok
 /\/ [analyzer] ErrorCode.BAD_THING /\/# 123: continued
-/\/ [cfe] Message.  /\/# named: compile-time error
-/\/ More message.  /\/#   another: ok
+/\/ [cfe] Message 1.  /\/# named: compile-time error
 /\/ [error line 12, column 34, length 56]  /\/# 3: continued
-/\/ [cfe] Message.
+/\/ [cfe] Message 2.
 """, [
     makeError(
         line: 1, column: 9, length: 3, analyzerError: "ErrorCode.BAD_THING"),
-    makeError(
-        line: 1, column: 9, length: 3, cfeError: "Message.\nMore message."),
-    makeError(line: 12, column: 34, length: 56, cfeError: "Message."),
+    makeError(line: 1, column: 9, length: 3, cfeError: "Message 1."),
+    makeError(line: 12, column: 34, length: 56, cfeError: "Message 2."),
   ]);
 
   // Allow front ends in any order.